In the field of magnetic tapes, investigations are recently being made enthusiastically on magnetic tapes as external storages for recording computer data (the so-called backup tapes), with the spread of minicomputers, personal computers, and office computers such as work stations. Especially in magnetic tapes for serves where large quantities of data are dealt with, the so-called linear serpentine mode has been put to practical use, in which signals are bidirectionally recorded/reproduced along the tape machine direction so as to heighten the speed of data processing. For practically using magnetic tapes in such applications, there is an especially strong desire for an improvement in recording capacity for attaining an increased recording capacity and a reduced recording-medium size, besides the desire for a size reduction and an increase in information-processing ability in computers.
Magnetic recording media heretofore in wide use comprise a nonmagnetic support and, formed thereover by coating, a magnetic layer comprising a binder and dispersed therein iron oxide, cobalt-modified iron oxide, CrO2, ferromagnetic metal particles, or hexagonal-ferrite particles. Of these magnetic materials, fine particles of hexagonal ferrites are known to have excellent high-density recording characteristics. However, in recording/reproducing with an inductive head which has hitherto been mainly used in the systems employing flexible media, the fine particles of a hexagonal ferrite have a low saturation magnetization and a sufficient output has not been obtained therewith.
In the removable recording employing such flexible media, however, the magneto resistive heads (MR heads) in use with hard disks have come to be used.
Since MR heads have high sensitivity, a sufficient reproduction output is obtained even with use of fine particles of a hexagonal ferrite. It is known that due to the noise reduction characteristic of hexagonal ferrites, a high C/N ratio is obtained. For example, Japanese Patent Application (Laid-Open) Nos. 342515/1994 and 302243/1998 disclose a technique which employs fine particles of barium ferrite (BaFe) and uses an MR head for reproduction.
However, since the well-known hexagonal-ferrite fine particles such as those shown above not only have a tabular shape but have an axis of easy magnetization perpendicular to the plane, the tabular particles are oriented, by calendering during the production of coated-type magnetic tapes, so that the tabular planes become parallel to the tape machine direction. As a result, the amount of magnetization components perpendicular to the magnetic plane is increased. The isolated pulse waveform becomes asymmetrical due to the perpendicular magnetization components and the reproduction output hence changes with the direction of reproduction. Namely, the related-art magnetic recording medium employing fine particles of a hexagonal ferrite is unsuitable for use in recording/reproducing in the linear serpentine mode.
Furthermore, even when that magnetic recording medium of the related art is used in a mode other than the linear serpentine mode, such as, e.g., helical scan mode, the results are an increased peak shift in high-density recording due to waveform interference and the necessity of waveform equalization.